Method and apparatus for incorporating a low contrast interface and a high contrast interface into an optical device

ABSTRACT

Methods and apparatuses for incorporating low contrast and high contrast interfaces in optical devices. In one embodiment an insulator is disposed proximate to a plurality of regions of a semiconductor including regions through which an optical beam is directed. High contrast interfaces are defined between the semiconductor and the insulator. Low contrast interfaces are defined between a doped region and the semiconductor. The optical beam is directed through the doped region from one of the plurality of semiconductor regions to another of the plurality of regions with relatively low loss. Optical coupling or evanescent coupling depending on an incident angle of the optical beam relative to the low contrast interface may occur through the doped region and low contrast interface.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to optical devices and,more specifically, the present invention relates to incorporating lowcontrast interfaces and high contrast interfaces in optical devices.

[0003] 2. BACKGROUND INFORMATION

[0004] The need for fast and efficient optical-based technologies isincreasing as Internet data traffic growth rate is overtaking voicetraffic pushing the need for optical communications. Commonly usedoptical devices include diffraction gratings, thin-film filters, fiberBragg gratings, and arrayed-waveguide gratings.

[0005] Inherent properties of materials may limit the manufacture anduse of many optical devices. As a result, producing such optical devicescan often be highly expensive and time consuming. Common problemsinclude high loss environments or a combination of materials that offerlittle control over the optical properties of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present invention is illustrated by way of example and notlimitation in the accompanying figures.

[0007]FIG. 1A is a diagram illustrating an embodiment of an opticaldevice including low and high contrast interfaces in accordance with theteachings of the present invention.

[0008]FIG. 1B is a diagram illustrating another embodiment of an opticaldevice including low and high contrast interfaces in accordance with theteachings of the present invention.

[0009]FIG. 2 is a diagram illustrating one embodiment of an opticaldevice with low and high contrast interfaces included in a Bragg gratingin accordance with the teachings of the present invention.

[0010]FIG. 3 is a diagram illustrating one embodiment of an opticaldevice with low and high contrast interfaces included in a directionalcoupler in accordance with the teachings of the present invention.

[0011]FIG. 4 is a diagram illustrating one embodiment of an opticaldevice with low and high contrast interfaces included in a ringresonator in accordance with the teachings of the present invention

[0012] FIGS. 5A-5F illustrates an embodiment of a process involving ionimplantation used to form an optical device such as the Bragg gratingillustrated in FIG. 2 in accordance with the teachings of the presentinvention.

[0013] FIGS. 6A-6E illustrates an embodiment of a process involvingepitaxial growth used to form an optical device such as the Bragggrating illustrated in FIG. 2 in accordance with the teachings of thepresent invention.

[0014]FIG. 7 is a diagram illustrating one embodiment of an opticalcommunication system including an optical device having low and highcontrast interfaces in accordance with the teachings of the presentinvention.

DETAILED DESCRIPTION

[0015] Methods and apparatuses for incorporating low contrast and highcontrast interfaces in optical devices are disclosed. In the followingdescription numerous specific details are set forth in order to providea thorough understanding of the present invention. It will be apparent,however, to one having ordinary skill in the art that the specificdetail need not be employed to practice the present invention. In otherinstances, well-known materials or methods have not been described indetail in order to avoid obscuring the present invention.

[0016] Reference throughout this specification to “one embodiment” or“an embodiment” means that a particular feature, structure orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily all referringto the same embodiment. Furthermore, the particular features, structuresor characteristics may be combined in any suitable manner in one or moreembodiments.

[0017] In one embodiment of the present invention, an optical devicehaving low and high contrast interfaces is provided. Embodiments of theoptical device offer fine control and low optical loss environments. Inone embodiment, a high contrast interface is provided with an insulatormaterial next to a core semiconductor material, where the insulator andthe semiconductor material have substantially different refractiveindexes from each other. The interface between the two materials thusdefines the high contrast interface. For example, the core semiconductormaterial of a waveguide may include silicon having an index ofrefraction of 3.5, while the surrounding cladding includes an insulator,such as an oxide, having an index of refraction of 1.5. In general, ahigh contrast interface may correspond to a range of differences inindices of approximately Δn>0.5. It is appreciated that other valueranges for Δn may be utilized in accordance with the teachings of thepresent invention and that Δn>0.5 is provided herewith for explanationpurposes. Thus, in the example above, the change in refractive indexesor Δn, is 2, generally considered as a high contrast interface. Such asystem has benefits according to embodiments of the present invention.For example, because the core semiconductor material has a highrefractive index relative to the cladding, light tends to stay in thecore while the insulator serves as a low loss cladding regionsurrounding the core. The ability to more tightly confine light to thecore allows an optical system to be made in more compact form accordingto embodiments of the present invention. Limitations of high contrastinterfaces may include a high coupling loss and scattering caused byroughness.

[0018] Accordingly, embodiments of the present invention also includelow contrast interfaces. Such an interface may be defined at theinterface between a region having a refractive index slightly differentfrom an adjacent or proximately disposed region. In one embodiment, thechange in refractive indexes may be in the range of a Δn ofapproximately 10⁻¹ -10 ⁻³. As stated, embodiments of the presentinvention provide a combination of both low and high contrast interfacesin the same optical device. The low contrast interface offers a lowerlevel of reflectivity, low loss, and fine control for an optical devicewhile the high contrast interfaces offer the benefits as describedabove. As will be discussed, examples of optical devices where both highcontrast interfaces and low contrast indexes are helpful include, butare not limited to, Bragg gratings, ring resonators, directionalcouplers or other suitable devices.

[0019] In one embodiment of the present invention, an optical devicehaving a low contrast interface system is incorporated into a highcontrast interface system. As will be discussed, a method of making thesame is also provided. In one embodiment a semiconductor material, suchas for example silicon, is doped with a dopant material, such as forexample, germanium in a high contrast interface system to provide adoped region and a low contrast interface between the semiconductormaterial and the doped region.

[0020]FIG. 1A is a diagram illustrating an embodiment of an opticaldevice including low and high contrast interfaces in accordance with theteachings of the present invention. In FIG. 1A an optical device 100includes insulator regions 106 and 108 disposed proximate to a pluralityof semiconductor regions 102 and 104 through which an optical beam 101is directed. Insulator regions 106 and 108 have a refractive indexsubstantially different from the refractive index of semiconductorregions 102 and 104. An interface between insulator region 106 andsemiconductor region 102 thus defines a high contrast interface 103. Inone embodiment, semiconductor regions 102 and 104 include silicon havingan index of refraction of approximately n_(Si)=3.5 and insulator regions106 and 108 include an oxide having an index of refraction ofapproximately n_(Ox)=1.5. Thus, in one embodiment, the difference inrefractive indices is approximately Δn=n_(Si)−n_(Ox)=2, which isconsidered a high contrast interface.

[0021] In one embodiment a doped region 105 is disposed betweensemiconductor regions 102 and 104. Doped region 105 has a refractiveindex slightly different than the refractive index of semiconductorregions 102 and 104. In general, a low contrast interface may correspondto a range of differences in indices of approximately Δn=10⁻¹ -10 ⁻³.For example, in one embodiment, doped region 105 may have an index ofrefraction of n_(d)=3.55. Since silicon has an index of refraction of3.5, the change in refractive indexesΔn_(eff)=n_(d)−n_(Si)=3.55−3.5=.05, defining low contrast interfaces110(a) and 110(b) between doped region 105 and semiconductor regions 102and 104, respectively. It is appreciated that other value ranges for Δnmay be utilized in accordance with the teachings of the presentinvention and that 10⁻¹ -10 ⁻³ is provided herewith for explanationpurposes.

[0022] Because semiconductor region 102 has a relatively high refractiveindex relative to insulator region 106, beam 101 stays confined tosemiconductor region 102 at high contrast interface 103. As mentionedpreviously, one of the many advantages to a high contrast interfaceincludes an ability to more tightly confine light to the semiconductorregion allowing the optical device to be made in more compact form.

[0023] In one embodiment, optical device 100 allows evanescent couplingto occur depending on an incident angle of optical beam 101 relative tolow contrast interface 110(a). For purposes of the disclosure, anincident angle θ is the angle that an optical beam makes with animaginary line perpendicular to a surface or interface at the point ofincidence. When the angle of incidence is less than the critical angle,(where the critical angle is defined as θ_(c)=Sin⁻¹ (n_(d)/n_(Si)) wheren_(Si)>n_(d)), light is generally optically coupled to be directedbetween semiconductor regions 102 and 104 through low contrastinterfaces 110(a) and 110(b) through doped region 105 with low loss inaccordance with the teachings of the present invention.

[0024] Even if the angle of incidence is greater than the critical angleθ_(c), however, some light is still optically coupled betweensemiconductor regions 102 and 104 though low contrast interfaces 110(a)and 110(b) and doped region 105 via evanescent coupling. Since therefractive indices n_(Si) and n_(d) are so close in value, n_(d/)n_(Si)approaches 1 and the critical angle θ_(c) is relatively large. Since Δnis relatively small in the illustrated embodiment, an optical beam evensubstantially parallel to the low contrast interface is evanescentlycoupled through doped region 105 to semiconductor region 104. Forexample, in the embodiment illustrated in FIG. 1A, optical beam 101 isdirected through semiconductor region 102 in a direction substantiallyparallel to low contrast interface 110(a), or with an incident angle 0substantially equal to 90 degrees which is greater than the criticalangle θ_(c). Nevertheless, evanescent coupling is provided through dopedregion 105 such that at least a portion of optical beam 111 is directedthrough semiconductor region 104 as a result. In sum, at least a portionof optical beam 101 is directed through doped region 105 betweensemiconductor regions 102 and 104 with optical coupling or evanescentcoupling, depending on the incident angle with low loss of the opticalbeam 101 relative to the low contrast interface 110(a) or 110(b).

[0025] In one embodiment, doped region 105 is designed to have athickness to allow evanescent coupling to semiconductor region 104 fromsemiconductor region 102 to occur through doped region 105. Thus, in anembodiment, evanescent coupling may occur when the incident angle θ ofoptical beam 101 to low contrast interface 110(a) is less than or equalto 90 degrees.

[0026]FIG. 1B is a diagram illustrating another embodiment of an opticaldevice including low and high contrast interfaces in accordance with theteachings of the present invention. In one embodiment an insulatorregion 126 is disposed proximate to a plurality of semiconductor regions122 and 124 through which an optical beam 120 is directed. In oneembodiment, insulator region 126 includes oxide and semiconductorregions 122 and 124 include silicon. Insulator region 126 has arefractive index n_(Ox) substantially different from the refractiveindex n_(Si) of semiconductor regions 122 and 124. An interface betweeninsulator region 126 and semiconductor regions 122 and 124 thus definesa high contrast interface 123. Because semiconductor region 122 has arelatively high refractive index relative to insulator region 126,optical beam 120 tends to remain confined in semiconductor region 122 athigh contrast interface 123. In one embodiment a doped region 125 isdisposed in between semiconductor regions 122 and 124. Doped region 125has a refractive index slightly different than the refractive index ofsemiconductor regions 122 and 124, defining low contrast interfaces121(a) and 121(b) between doped region 125 and semiconductor regions 122and 124. Thus, in one embodiment, optical beam 120, may travel fromsemiconductor region 122 through doped region 125 to semiconductorregion 124 where a small effective refractive index difference isprovided at interfaces 121(a) and 121(b).

[0027] In one embodiment, the incident angle of beam 120 relative to lowcontrast interface 121(a) is greater than or equal to 0 degrees, andbeam 120 may travel through doped region 125 to reach semiconductorregion 124. In one embodiment, the refractive index of doped region 125is carefully controlled such that the reflectivity at low contrastinterfaces 121(a) and 121(b) is carefully controlled. As will bediscussed, the refractive index of doped region 125 is determined byincluding a controlled concentration of a dopant material in dopedregion 125. In one embodiment, the dopant material provides a controlledrefractive index for doped region 125 as well as low optical loss foroptical beam 120 when directed through doped region 125. In oneembodiment the optical device described above is similar to anembodiment of a Bragg grating that will be discussed below in referenceto FIG. 2.

[0028] In the above examples discussed in FIGS. 1A and 1B it isappreciated that silicon is an example material provided for explanationpurposes and that other semiconductor materials including for exampleIndium Phosphide (InP), Gallium Arsenide (GaAs) or other III-Vsemiconductor materials may be utilized in accordance with the teachingsof the present invention. Furthermore, in one embodiment, the insulatorregions may be an oxide such as silicon dioxide (SiO₂). In anotherembodiment, the insulator regions may be a nitride or other suitableinsulator.

[0029]FIG. 2 is a diagram illustrating a cross section of one embodimentof an optical device with low and high contrast interfaces included in awaveguide Bragg grating in accordance with the teachings of the presentinvention. In one embodiment, waveguide Bragg grating 200 includes aplurality of doped regions 218 each similar to doped region 125 of FIG.1B. Accordingly, low contrast interfaces are provided along thewaveguide at each interface between doped regions 218 and semiconductorregion 213. In the illustrated embodiment a semiconductor-basedwaveguide Bragg grating 200 is disposed on a wafer 210. In oneembodiment, wafer 210 is a silicon-on-insulator (SOI) wafer having highcontrast interfaces defined between the semiconductor regions and theinsulator regions. As illustrated in FIG. 2, wafer 210 includes aninsulator region 216. Below insulator region 216 is a semiconductorregion 213 and semiconductor region 215 in accordance with the teachingsof the present invention. Between regions 213 and 215 there is a buriedinsulator layer 214 that integrally bonds semiconductor layers 213 and215. In one embodiment, semiconductor layers 213 and 215 include siliconand insulators 214 and 216 may be an oxide, such as silicon dioxide(SiO₂).

[0030] In one embodiment, the low contrast interfaces provided along thewaveguide at each interface between doped regions 218 and semiconductorregion 213 provide periodic or quasi-periodic perturbations in aneffective index of refraction provided along an optical path. As aresult, a multiple reflection of an optical beam 217 traveling along anoptical path 212 occurs at the interfaces between semiconductor region213 and the plurality of doped regions 218 along an optical path 212. Inone embodiment, a Bragg reflection occurs at a particular or Braggwavelength. Accordingly, the Bragg wavelength may be filtered or droppedfrom the optical beam 217.

[0031]FIG. 3 is a diagram illustrating another embodiment of an opticaldevice with low and high contrast interfaces included in a 3 dB ordirectional coupler 300 in accordance with the teachings of the presentinvention. Directional coupler 300 includes two adjacent waveguides 302and 304 and a doped region 305 disposed between waveguides 302 and 304in accordance with the teachings of the present invention. In oneembodiment, directional coupler 300 uses evanescent coupling to transfera portion of optical beam 308 from waveguide 302 to waveguide 304. Anarea denoted by dotted lines 312 on directional coupler 300 correspondsto device 100 of FIG. 1A and its accompanying discussion of the effectof the low contrast interfaces and high contrast interfaces included inthe device.

[0032] Low contrast interfaces between doped region 305 and waveguides302 and 304 allow evanescent coupling to occur in a high contrastenvironment. In a directional coupler in a high contrast only system,the two adjacent waveguides are placed very close together to allow someof the light to transfer between waveguides. However, in one embodimentof the present invention, including doped region 305 and low contrastinterfaces between waveguides 302 and 304 permits evanescent coupling tooccur without the need for waveguides 302 and 304 to be so close to oneanother, thus reducing strain on the manufacturing process.

[0033]FIG. 4 is a diagram illustrating yet another embodiment of anoptical device with low and high contrast interfaces included in a ringresonator 400 in accordance with the teachings of the present invention.In one embodiment, ring resonator 400 includes waveguides 402 and 404and a ring waveguide 406 included in an insulator region 407. Waveguides402 and 404 and ring waveguide 406 include a semiconductor region. Inone embodiment the semiconductor region includes silicon. On opposingsides of ring waveguide 406 and proximately disposed to each waveguide402 and 404 are doped regions 405 and 410, respectively. In operation,an optical beam 408 travels along waveguide 402, light from beam 408 isthen transferred via evanescent coupling from waveguide 402 via dopedregion 405 to ring waveguide 406. Regions 412 and 412′ correspond to thediscussion in relation to FIG. 1A and its accompanying discussion of theeffect of the low contrast interfaces and high contrast interfacesincluded in the device. In one embodiment, ring waveguide 406 isdesigned to have one or more resonant wavelengths such that a resonatedoptical beam 406 having the one or more resonant wavelengths may beevanescently coupled to waveguide 408 at region 412′ to waveguide 404.It is appreciated that although a ring resonator is specifically shown,in one embodiment, a disk resonator may also utilize low and highcontrast interfaces in accordance with embodiments of the presentinvention.

[0034] It is appreciated that the example waveguide Bragg grating, thedirectional coupler and ring resonator are examples of optical devicesprovided herewith for explanation purposes. Other suitable devices withlow and high contrast interfaces may be utilized in accordance withembodiments of the present invention. The doped regions of the exampleoptical devices illustrated in FIGS. 2-4 above may in an embodimentinclude germanium. For example, the addition of germanium to silicon,resulting in an alloy, changes the refractive index of the material. Thechange in index is dependent on the amount of germanium and the strainof the material.

[0035] If strain is neglected, the index follows the form of:

n(Si_(1-x)Ge_(x))=n(Si)+ax, where a≈0.8 for λ≈1310-1550 nm,

[0036] and when strain is considered, follows the form:

n(Si_(1-x)Ge_(x))=n(Si)+ax+bx ², where a≈0.3 and b≈0-0.3

[0037] Therefore, small amounts of germanium can give a small change inthe refractive index (Δn≈10⁻³ to 10⁻¹). Periodic changes in therefractive index profile can result in a Bragg grating such as forexample, the embodiment illustrated in FIG. 2, which may be used for astatic or tunable filter, or in part of a circulator or laser cavity, orother suitable device.

[0038] FIGS. 5A-5E illustrate an embodiment of a process involving ionimplantation used to form an optical device such as for example, Bragggrating 200 illustrated in FIG. 2 in accordance with the teachings ofthe present invention. In one embodiment, a wafer 500 can include an SOIwafer. In one embodiment, wafer 500 includes high contrast interfaceswith a top insulator region 504 above semiconductor region 506 and aburied insulator region 508 between semiconductor regions 506 and 510.

[0039] In FIG. 5A, a photoresist layer 502 has been deposited overinsulator region 504. In one embodiment, each trench 512 corresponds toa doped region to be formed. In one embodiment, photoresist layer 502has been deposited via a spin-on deposition process to define areas inwhich one or more doped regions will be formed to provide one or morelow contrast interfaces. As shown in the depicted embodiment,photoresist layer 502 has been patterned and etched to create a seriesof periodic trenches 512 exposing discrete transverse sections ofinsulator region 504. In one embodiment, the patterning is done usingstandard lithographic techniques well known in the art, which typicallycomprise depositing layers of the correct materials on the device,applying a photoresist on the wafer, exposing the photoresist in areasto be added (light mask) or removed (dark mask) and then performing theappropriate etch. In one embodiment, a hard mask may also be used.

[0040] In one embodiment, the patterning is carried out using thelithographic process described above although other patterning processessuch as ablation, ruling, or other techniques will be apparent to thoseskilled in the art. The etching can be carried out using either a dry ora wet process, and varieties of both wet and dry etching will beapparent to those skilled in the art and may be dependent upon thematerials used for photoresist layer 502 and insulator region 504.

[0041] Next, as illustrated in FIG. 5B, exposed discrete transversesections 514 of insulator region 504 have been removed by selective wetor dry etching. In one embodiment, discrete transverse sections ofsemiconductor region 506 are now exposed. Again, a lithographicpatterning process may be used and wet or dry etching processes may beused. In one embodiment, insulator region 504 may serve as a hard maskfor the implantation of Ge ions.

[0042] In FIG. 5C photoresist layer 502 has been removed and Ge ionimplantation takes place with insulator region 504 as a hard mask.Although in this example, germanium is implanted, other materials, suchas for example, aluminum, carbon, indium, phosphorus, boron or othersuitable dopant material, or combinations thereof, may also beimplanted. One advantage of Si_(1-x)Ge_(x) is that it is an alloy, whichmeans that a second phase of material will not precipitate out. Such aninterface of a new phase could then serve as a scattering site,increasing the loss of the material. With the implantation of certainother ions, Boron, for instance, optical losses may be incurred becausefree carriers have been introduced.

[0043] In one embodiment, ion implantation at multiple energies andangles is performed to give a uniform cross-section to the impuritydistribution in traverse sections 528 of semiconductor region 506.Accordingly, multiple ion implantations can be performed in order toachieve a non-Gaussian dependent distribution of ions. In oneembodiment, the germanium concentration employed to achieve a reasonableefficiency grating is approximately 0.5 to 5%, which roughly correlatesto the same Δn that is used in fiber gratings based on silica. Higherconcentrations may be used as long as considerations of strain,relaxation and loss are taken into account. Generally, only lowconcentrations such as 20% or more Ge are utilized for the opticaldevice in accordance with the teachings of the present invention. Thus,as an example, energy of 400 keV and a dose of 3×10¹⁶/cm² may result inan alloy with a peak concentration of 2.6% approximately 0.25 μm belowthe surface. At this energy, however, the implanted area is amorphizedand solid phase epitaxy may be used to heal the damage. This stage ofsolid phase epitaxy (SPE) or regrowth is illustrated in FIG. 5D. The SPEis typically performed at low temperatures (<600 C.°), althoughtemperatures of 700 C.°-900 C.° or other suitable temperature ranges maybe used.

[0044] Finally, in FIGS. 5E and 5F a waveguide is patterned and etchedin wafer 500. FIG. 5F is a cross-sectional view of the wafer afteretching and FIG. 5E illustrates a top view of the wafer after etching.Again, a lithographic patterning process may be used and wet or dryetching processes may be used.

[0045] FIGS. 6A-6D illustrate another embodiment of a process involvingepitaxial growth used to form an optical device such as Bragg grating200 illustrated in FIG. 2 in accordance with the teachings of thepresent invention. One advantage of epitaxial growth over ionimplantation may be that epitaxial growth may achieve a doping region ofgreater depth in a wafer. FIG. 6A is a cross-sectional view of a wafer600 including a top insulator region 620 and semiconductor regions 630and 650. Between semiconductor region 630 and 650 is a buried insulatorregion 640.

[0046] In one embodiment, semiconductor regions 630 and 650 includesilicon and insulator regions 620 and 640 include silicon dioxide(SiO₂). In FIG. 6A, a photoresist layer 660 has been deposited overinsulator region 620.

[0047] In one embodiment, photoresist layer 660 has been deposited usingfor example, a spin-on deposition process. As shown, photoresist layer660 has been patterned and etched to create a series of periodictrenches 670. As in the process illustrated in FIGS. 5A-5E, a hard maskmay also be used in one embodiment. In one embodiment, the patterningmay be carried out using a lithographic process although otherpatterning processes such as ablation, ruling, or other techniques willbe apparent to those skilled in the art. The etching can be carried outusing either a dry or a wet process, and varieties of both wet and dryetching will be apparent to those skilled in the art and may bedependent upon the materials used for photoresist layer 660 andinsulator region 620.

[0048] As shown in FIG. 6A, discrete transverse sections 690 ofinsulating layer 620 are exposed by the patterned photoresist layer 660.In one embodiment, insulator region 620 forms a hard mask oversemiconductor substrate layer 630. Discrete sections of insulator region620 exposed by etching appear at locations 690.

[0049] Next, as illustrated in FIG. 6B, the hard mask or insulatorregion 620 and semiconductor region 630 are removed by selective wet ordry etching. In one embodiment a reactive ion etch may be used. Again, alithographic patterning process may be used and wet or dry etchingprocesses may be used. As a result, periodic trenches are formed atlocations 680. In one embodiment, trenches 680 have a depth order of ˜2μm.

[0050] In FIG. 6C, photoresist layer 660 is removed and Si_(1-x)Ge_(x)is epitaxially grown in trenches 680. Standard chemical vapor deposition(CVD) processes may be used to grow the Si_(1-x)Ge_(x) in the trenches680. Finally, in FIGS. 6D and 6E, a waveguide is patterned and etched.In one embodiment, trenches of up to ˜2 μm are etched.

[0051] In the processes illustrated above in FIGS. 5A-5F and 6A-6E,semiconductor regions have included silicon as an example. It isappreciated that silicon is an example material provided for explanationpurposes and that other semiconductor materials including III-Vsemiconductor materials or the like may be utilized in accordance withthe teachings of the present invention. For instance, in one embodimentthe semiconductor material includes gallium arsenide. Furthermore, inone embodiment, the dopant material may include at least one ofaluminum, indium, antimony or phosphorus or other suitable material. Inone embodiment the insulator regions may be an oxide such as silicondioxide (SiO₂). In another embodiment, the insulator regions may includenitride or other suitable insulator.

[0052] The above embodiments of processes illustrated in FIGS. 5 and 6illustrate a Bragg grating, however, other optical devices having lowcontrast and high contrast interfaces may be produced in a similarmanner.

[0053]FIG. 7 is a diagram illustrating one embodiment of an opticalcommunication system 700 including a low contrast/high contrast opticaldevice 704 in accordance with the teachings of the present invention. Invarious embodiments optical device 704 may be included in a waveguideBragg grating, a directional coupler, a ring resonator or anotheroptical device in which low contrast and high contrast interfaces areincluded. In the depicted embodiment, optical communication system 700includes an optical transmitter 702 to transmit an optical beam 708. Anoptical receiver 706 is optically coupled to receive optical beam 708.It is appreciated that optical transmitter 702 and optical receiver 706may also include optical transceivers and therefore have bothtransmitting and receiving capabilities for bi-directionalcommunications. In one embodiment, optical device 704 is opticallycoupled between optical transmitter 702 and optical receiver 706. In theillustrated embodiment, optical device 704 is shown to be at thereceiving end of optical communication system 700. In other embodiments,optical device 704 may be disposed at various locations along atransmission path or at the transmitting end of optical communicationsystem 700.

[0054] In one embodiment, optical device 704 may be included in a Bragggrating or ring resonator and be utilized in for example an add/dropfilter enabling the addition or extraction of a channel from a wavedivision multiplexed (WDM) optical beam 708 transmitted from opticaltransmitter 702 along an optical path. Thus, an optical beam 710 havinga specific wavelength is output from optical device 704. In anotherembodiment, optical device 704 may include a 3 dB coupler or directionalcoupler and may be used to split optical beam 708 such that a duplicateoptical beam 710 is output from optical device 704 and optical beam 708is received at optical receiver 706.

[0055] In the foregoing detailed description, the method and apparatusof the present invention have been described with reference to specificexemplary embodiments thereof. It will, however, be evident that variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the present invention. The presentspecification and figures are accordingly to be regarded as illustrativerather than restrictive.

What is claimed is:
 1. An apparatus, comprising: a semiconductormaterial including a plurality of regions through which an optical beamis directed; an insulator disposed proximate to the plurality of regionsof semiconductor, the insulator having a refractive index substantiallydifferent than a refractive index of the semiconductor material, suchthat high contrast interfaces are defined between the semiconductormaterial and the insulator; and a doped region disposed between at leasttwo of the plurality of regions of semiconductor material, the dopedregion including the semiconductor material and a dopant material andhaving a refractive index slightly different than the refractive indexof the semiconductor material, such that low contrast interfaces aredefined between the semiconductor material and the doped region, theoptical beam to be directed through the doped region from one of theplurality of regions to another of the plurality of regions with atleast one of optical coupling or evanescent coupling depending on anincident angle of the optical beam relative to the low contrastinterface.
 2. The apparatus of claim 1 wherein the incident angle of theoptical beam relative to the low contrast interface is greater than orequal to zero degrees.
 3. The apparatus of claim 1 wherein the incidentangle of the optical beam relative to the low contrast interface is lessthan or equal to ninety degrees.
 4. The apparatus of claim 1 wherein thesemiconductor material includes silicon.
 5. The apparatus of claim 4wherein the dopant material includes germanium.
 6. The apparatus ofclaim 1 wherein the semiconductor material includes an III-V material.7. The apparatus of claim 6 wherein the semiconductor material includesgallium arsenide.
 8. The apparatus of claim 7 wherein the dopantmaterial includes one of aluminum, carbon, indium or phosphorus.
 9. Theapparatus of claim 1 wherein the dopant material is implanted into thesemiconductor material.
 10. The apparatus of claim 1 wherein the dopedregion is epitaxially grown in the semiconductor material.
 11. Theapparatus of claim 1 wherein the apparatus includes a Bragg grating. 12.The apparatus of claim 1 wherein the apparatus includes at least one ofa ring resonator and a disk resonator.
 13. The apparatus of claim 1wherein the apparatus includes a directional coupler.
 14. A method,comprising: patterning a mask on a wafer including first and secondinsulating layers and first and second semiconductor materials, thefirst semiconductor material disposed between the first and secondinsulating layers, the second insulating layer disposed between thefirst and second semiconductor materials, the wafer including a highcontrast interface located at an interface between the firstsemiconductor material and at least one of the first and secondinsulating layers, wherein the mask is patterned to define a locationfor a doped region in the first semiconductor material; implanting acontrolled concentration of dopant material ions into the firstsemiconductor material to form the doped region in the firstsemiconductor material such that a low contrast interface is defined atan interface between the first semiconductor material and the dopedregion such that an optical beam is directed through the doped regionfrom first semiconductor material with at least one of optical couplingor evanescent coupling depending on an incident angle of the opticalbeam relative to the low contrast interface.
 15. The method of claim 14further comprising regrowing amorphized regions of the wafer using solidphase epitaxy.
 16. The method of claim 14 wherein patterning the maskcomprises etching the first insulating layer to form a hard mask. 17.The method of claim 14 wherein patterning the mask comprises patterninga photoresist layer to form the mask.
 18. A method, comprising:patterning a mask on a wafer including first and second insulatinglayers and first and second semiconductor materials, the firstsemiconductor material disposed between the first and second insulatinglayers, the second insulating layer disposed between the first andsecond semiconductor materials, the wafer including a high contrastinterface located at an interface between the first semiconductormaterial and at least one of the first and second insulating layers,wherein the mask is patterned to define a location for a doped region inthe first semiconductor material; etching a trench into the firstsemiconductor material at the location for the doped region; and growingthe doped region in the trench in the semiconductor material, the dopedregion having a controlled concentration of dopant material insemiconductor material such that a low contrast interface is defined atan interface between the first semiconductor material and the dopedregion such that an optical beam is directed through the doped regionfrom the first semiconductor material with at least one of opticalcoupling or evanescent coupling depending on an incident angle of theoptical beam relative to the low contrast interface.
 19. The method ofclaim 18 wherein patterning the mask comprises etching the firstinsulating layer to form a hard mask.
 20. The method of claim 18 whereinpatterning the mask comprises patterning a photoresist layer to form themask.
 21. A method, comprising: directing an optical beam through afirst region of semiconductor material; confining the optical beam toremain in the semiconductor material with a high contrast interface;optically coupling the optical beam to a second region of semiconductormaterial through a low contrast interface and through a doped regiondisposed in the semiconductor material, the low contrast interfacedefined at an interface between the semiconductor material and the dopedregion; and evanescently coupling at least a portion of the optical beamto the second region of semiconductor material through the low contrastinterface and through the doped region disposed in the semiconductormaterial if an angle of incidence of the optical beam relative to thelow contrast interface is greater than a critical angle of the lowcontrast interface.
 22. The method of claim 21 further comprisingdirecting the optical beam through a plurality of low contrastinterfaces so as to reflect a wavelength of the optical beam matching aBragg condition.
 23. The method of claim 21 wherein evanescentlycoupling at least a portion of the optical beam to the second region ofsemiconductor material through the low contrast interface and through adoped region comprises directing a remaining portion of the optical beamthrough the first region of semiconductor material.
 24. A system,comprising: an optical transmitter to transmit an optical beam; anoptical receiver optically coupled to the optical transmitter to receivethe optical beam; and an optical device optically coupled between theoptical transmitter and the optical receiver, the optical deviceincluding a semiconductor material and having a high contrast interfaceand a low contrast interface, the high contrast interface defined at aninterface location between the semiconductor material and insulatingmaterial included in the optical device, the low contrast interfacedefined at an interface location between the semiconductor material anda doped region disposed in the semiconductor material, the optical beamdirected through the semiconductor material and confined to remain inthe semiconductor material with the high contrast interface, the opticalbeam optically coupled to propagate through the low contrast interface,the optical beam to propagate through the low contrast interfaces withevanescent coupling depending on an incident angle of the optical beamrelative to the low contrast interface.
 25. The system of claim 24wherein the semiconductor material includes silicon and the doped regionincludes silicon doped with germanium.
 26. The system of claim 24semiconductor material includes 111-V semiconductor material.
 27. Thesystem of claim 24 wherein the insulating material includes at least oneof oxide or nitride.
 28. The system of claim 24 wherein the opticaldevice is included in at least one of a waveguide Bragg grating, a ringresonator and a directional coupler.